Conveyor systems for sorting articles are well-known in the art. Such systems generally comprise a main conveyor and a laterally extending takeaway conveyor for receiving selected articles. In the typical main conveyor, the transport surface for supporting and carrying the articles is formed from a plurality of elongate slats. To provide the desired sortation function, diverters are mounted on the slats and travel along with the transport surface. These diverters move transverse to the direction of conveyor travel in response to guide means positioned under the transport surface. In traversing across the main conveyor, the diverters engage and direct selected articles to the takeaway conveyor, thereby providing the desired sortation function. The slats which form the transport surface are usually tubular and, thus, articles simply slide along the upper curved extent of the slats and onto the takeaway conveyor.
Such an arrangement works well for low-friction articles; that is, articles formed of materials that do not create any significant degree of static and/or sliding friction with the slats. However, the above-described arrangement is simply not effective for use with articles having high coefficients of static/sliding friction with the slats, such as rubber tires. With such high-friction articles, excessive force is required for the diverters to overcome this friction. This tends to induce vibration of the articles, due to the intermittent sticking and release as they are pushed laterally across the slats. In some instances, the vibration can result in the articles being displaced from the intended path to the takeaway conveyor causing disruption of the entire conveying process. Furthermore, this sticking and resultant vibrating action of the conveyed articles can cause deleterious wear on system components, and thus further decreases system efficiency.
To overcome these difficulties, others have proposed forming the slats of materials having a high degree of lubricity; i.e. using low-friction coatings on the slats. One example of such a proposal is described in U.S. Pat. No. 4,896,760 to Triantafilou et al. The specific solution proposed therein includes providing the slats of a sortation conveyor with either a low friction coating or a separate sleeve formed of such materials.
First of all, it should be appreciated that many such coatings simply do not provide the desired reduction in sliding friction for some articles. For example, a popular low-friction coating marketed under the trademark TEFLON.RTM. maintains a sliding coefficient of friction with rubber of around 1.0-1.5. For heavy rubber objects, such as tires, this is simply not a sufficient reduction in friction to produce efficient lateral sliding.
Moreover, even if a reduction in sliding friction is achieved, the coatings are expensive, as well as being expensive to apply. Adding to the shortcoming of these coatings for this purpose is the fact that the coatings will ultimately wear down over time, especially where heavy, high friction articles are being conveyed. Closely associated with wear is the monitoring required to ensure that optimum frictional characteristics are consistently maintained. Any spots where the coating wears off or is improperly applied requires attention, as the exposure of any significant area of a high friction surface can grab and possibly mar the article. This condition can also lead to disruption of the conveying cycle, and create the deleterious chatter, inefficiency, and wear on system components.
Accordingly, a need is identified for a sortation conveyor system having an improved transport surface for the main conveyor that overcomes the above-described limitations and disadvantages of the prior art. The hallmark of the transport surface would be the ability to support and carry articles in a forward direction, while also permitting substantially frictionless motion in a direction transverse to conveyor travel for diversion to a takeaway conveyor. Additionally, the surface would be substantially maintenance free, simple in design, and easy to retrofit onto existing sortation conveyor systems.